(1) Field of the Invention
This invention relates to acrylonitrile compound-styrene compound grafted polyphenylene oxides which have excellent solvent resistance and resistance to oxidation.
(2) Description of the Prior Art
Polyphenylene oxide (hereinafter referred to as PPO) is a resin having excellent heat resistance, mechanical properties and electrical properties. However, its solvent resistance (especially resistance to hydrocarbons) and resistance to oxidation are not adequate in some applications.
The resistance to oxidation is generally improved by incorporating polystyrene and an antioxidizing agent. For the solvent resistance, an effective method to improve it has not yet been proposed. This is because acrylonitrile-styrene (hereinafter referred to as AS) resins having excellent solvent resistance are not compatible with PPO and therefore the incorporation of an AS resin for the purpose of improving the solvent resistance of PPO would reduce the excellent mechanical properties inherent to PPO.
In order to overcome this disadvantage, attempts to graft-polymerize an acrylonitirle compound-styrene compound copolymer to PPO has been proposed. For example, they are disclosed in Japanese Patent Publication No. 38596/1977, Japanese Patent Application Laid-open No. 137130/1980 etc. However, the AS grafted PPO's described in these patents have only a low extent of modification.
In general, the extent of graft modification of PPO is evaluated by the time to form a precipitate when dissolving the graft modified PPO in methylene chloride. This method is called a methylene chloride test, and utilizes a phenomenon that PPO in methylene chloride solution forms a complex with said solvent and is rendered insoluble in said solvent to form a precipitate, and therefore no precipitate formation in this test is construed as meaning that the properties as PPO have been lost. The time to form a precipitate has a dependency on the molecular weight of PPO, and particularly when the number of the repeating units (n) of PPO is below 100, the time to precipitate is long.
In the published or laid-open patent applications hereinabove cited, the methylene chloride test was conducted in 3-24 hours. However, as the result of our detailed study, it has now been discovered that with the extent of modification such as that evaluated in such time period, the abovementioned resistance to oxidation and solvent resistance are practically inadequate. In other words, the AS grafted PPO has a low degree of graft modification, and its properties are similar to those of PPO, especially the resistance to oxidation cannot withstand practical use.
As the result of our study, it has now been found that in order to satisfy these resistances to oxidation and solvents, at least 48 hours is necessary before a precipitate is formed, and 72 hours or longer is especially preferred, and thus this invention has been achieved.